Friction-type draft gear assemblies have been in widespread use in the railroad industry for many years to absorb both buff and draft shocks applied to the railway rolling stock. Many of such draft gear assemblies which were in use, prior to the present invention, are taught in U.S. Pat. Nos. 2,916,163; 3,178,036; 3,447,693 and 4,645,187. Each of the above-identified patents is owned by the assignee of the present invention. The teachings of each of these patents are all incorporated into the present application by reference thereto.
It is known, for example, from U.S. Pat. No. 4,645,187 that to achieve a reduction in the weight of a railway car, regardless of the type of railway car to be considered, it is desirable to reduce the weight of the necessary auxiliary equipment disposed on such railway car to an absolute minimum. Each of the friction-type draft gear assemblies taught in U.S. Pat. Nos. 2,916,163; 3,178,036 and 3,447,693 have a weight of at least 386 pounds. There are a number of significant reasons why such lighter weight draft gear assemblies are desirable in the railroad industry. The first reason is that less energy is required to move the railway car over the track structure. A second reason is that additional pay load may be carried by such car without exceeding a load limit on a particular track structure and without incurring increased energy costs.
However, even though it has been known that such lighter weight draft gear assemblies were desirable for the above reasons, such a lighter weight draft gear assembly only became available with the invention taught in the above referenced U.S. Pat. No. 4,645,187. Nevertheless, regardless of the weight of such draft gear assembly, it must be capable of maintaining the minimum shock absorbing capacity during its service life. This minimum shock absorbing capacity is specified in the standards which have been established by the Association of American Railroads (AAR). See, for example, AAR specification M-901-E. This specification, for example, requires that these draft gear assemblies have a rated capacity of at least 36,000 foot pounds. Also, it is important to note that the action of the friction portion of such draft gear assembly permits this to be accomplished without exceeding a 500,000 pound reaction pressure being exerted on the car sills of a freight car. This is a requirement in order for the quite high energy shocks to be readily handled without upsetting the coupler shank.
Another serious problem that is associated with friction-type draft gear assemblies of all known prior art draft gear is the generally wide variance in the coefficient of friction that normally occurs between the friction elements disposed in such friction portion of the draft gear assemblies. This problem is made even worse by the environmental conditions in which these friction-type draft gear assemblies must operate. In addition to dust and dirt, the moisture present on the components can cause such components to rust if such draft gear assemblies are not in substantially constant use. It should be noted that the capacity of such friction-type draft gear assemblies can be greatly affected by such wide variance in the coefficient of friction of such friction elements.